1. Field of the Invention
The present invention relates generally to the field of cell and molecular biology and microbiology, and, more particularly to a bioreactor and related method. Although the invention is subject to a wide range of applications, it is especially suited for use in perfusion cell culture and bioartificial organs, and will be particularly described in that environment.
2. Description of the Related Art
Traditionally, cell have been grown on a nutrient medium spread over a two-dimensional plastic culture dish. Bioreactors provide an alternative means for culturing cells, which is more efficient and manageable.
Bioreactors come in many shapes and sizes, and serve various functions in addition to conventional cell culturing, including, artificial organs and bioremediation units. In conventional bioreactors, hollow fibers traverse the length of an enclosed cylindrical shell. A cell and culture medium mixture is injected into the shell. The cells typically settle on the outer surface of the hollow fibers. Nutrients and oxygen flow through the intracapillary space of the hollow fibers, and they diffuse across the walls of the hollow fibers to nourish the cells.
Current commercially available bioreactors typically require the user to seed the unit with the desired cells or tissue, as it is difficult for manufacturers of bioreactors to deliver a pre-fabricated bioreactor that contains viable cells or tissue. To offer a bioreactor with viable cells or tissue already in place, a manufacturer must somehow preserve the cells or tissue located within the shell, such that the cells remain temporarily inactive without destroying cell viability, and provide a mechanism for reactivating the cells. Such a result may be accomplished by rapidly and uniformly freezing the bioreactor, and thawing the bioreactor when it is ready to use. The freezing preferably should occur at a uniform and high cooling rate, also referred to as vitrification, because a non-uniform or low-rate freezing can lead to the creation of ice crystals, a byproduct which destroys a large number of cells, and incidently leads to fluid volume expansion which may burst the bioreactor.
The rapid uniform freezing or vitrification process, which maximizes cell viability, is not easily accomplished with conventional hollow-fiber bioreactors. For example, a typical bioreactor is approximately 3 to 4 inches in diameter and can be submerged into liquid nitrogen to freeze the bioreactor. This method, however, freezes the outer layer of liquid contained within the shell, which thus acts as an insulator, leaving the core, where the cells have settled, unfrozen.
Thus, a need exists for a desirable pre-fabricated, vitrified bioreactor seeded with viable cells or tissue that is in a ready-to-use state. Such a bioreactor can alleviate the nuisance and expense of the user having to assemble and seed the bioreactor, with its attendant sterility and fabrication requirements, whether used for cell culture, biomedical, or other purposes.